FCA Comments regarding the proposed NMFS Horizontal Screen Criteria:
11.6.1.7 Horizontal Screens: Horizontal screens have been evaluated as experimental technology,
because they operate fundamentally different than conventional vertically oriented screens. This
fundamental difference relates directly to fish safety, because when inadequate flow depth exists with
vertically oriented screens, there is no potential for fish to get trapped over the screened surface. In
contrast, when water level on horizontal screens drops and most or all diverted flow goes through the
screens, there is high likelihood that fish will become impinged and killed on the screened surface. In
addition, if depths become shallow and flow rate is high over a horizontal screen, the resulting crosssection velocity may be too high to allow fish to swim away from the horizontal screen surface.
FCA Comment: This opening statement is not correct. Horizontal screens are fundamentally
different than vertically oriented screens in how they function; however, they are not different from
conventional screens in the fact that, if they are operated outside of their design parameters, they
could potentially harm fish. Why else would there be criteria for design of all screen types? With the
current design (influenced by lessons learned from the Widows Creek screen), it is impossible for
“most or all of the diverted flow” to go through the screens, due to the sealed weir wall. Instead,
most or all of the flow goes to bypass. ODFW staff members have observed this at screens with
sealed weir walls. In addition, with a sealed weir wall, the minimum depth over the screen is fixed.
If the depth over the screen is less than that of the weir wall height, then all of the flow is going to
bypass and the approach velocity is zero. In that case, fish are simply in a flume that carries them
back to the stream via the bypass.
Horizontal screens are considered to biologically equivalent to conventional screens only if the
following criteria and guidelines are achieved in design and operation:
11.6.1.7.1 Design Development: Since site-specific design considerations are required,
NMFS engineers must be consulted throughout the development of the horizontal screen
design.
FCA Comment: All screen types have site specific design considerations such as inlet
structures, flow volumes, bypass design, orientation, elevations, power sources, frequency of
active cleaning, etc. This is not unique to horizontal screens and therefore horizontal screens
should not be held to a higher standard. This essentially, and unnecessarily, keeps horizontal
screens in a perpetual state of “experimental status” and therefore ensuring higher project
costs, longer timelines, and a competitive disadvantage.
11.6.1.7.2 Hydrologic and Hydraulic Analysis: The horizontal screen design process must
include an analysis to verify that sufficient hydrologic and hydraulic conditions exist in the
stream so as not to create a passage impediment in the stream channel (see Section 4.1), or
in the off-stream conveyance, including the screen and bypass. This analysis must conclude
that all criteria listed below can be achieved for the entire juvenile outmigration. If the
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following criteria cannot be maintained per this design analysis, a horizontal screen design
must not be used at the site.
FCA Comment: Is there a definition of what the analysis would consist of? Is this saying that
if a passage barrier already exists in the stream, then a horizontal screen can’t be
considered? Is this saying that there are different criteria during juvenile outmigration?
Shouldn’t this be a requirement for all screen designs?
11.6.1.7.3 Screen Geometry: Horizontal screens must be set at slopes and other geometry
consistent with prototypes developed through conducted research and/or associated
physical models. The screen designer must provide evidence of research or an example site
that confirms the adequacy of the design.
FCA Comment: Is this merely saying that the proposed horizontal screen design must have
been tested and shown to be similar to the design for a particular site? Would a screen such
as the Farmers Screen need to show that research (and develop a prototype) for every
potential screen site? There is a lot of ambiguity in this section which inevitably leads to
differing application standards depending on who is reviewing the project.
11.6.1.7.4 Site Limitation: Horizontal screens must not be used in stream or river channels.
11.6.1.7.5 Flow Regulation: For a horizontal screen to be installed, the site must have a good
head gate, capable of maintaining sufficiently consistent diversion rates to allow a horizontal
screen and bypass to operate within these criteria and guidelines.
11.6.1.7.6 Channel Alignment: Horizontal screens must be installed such that the
approaching conveyance channel is completely parallel and in line to the screen channel (no
skew) for at least twenty feet or two screen channel lengths upstream of the screen civil
works (whichever is greater). Horizontal screens must be installed such that a smooth
hydraulic transition occurs from the approach channel to the screen channel (no abrupt
expansion or contraction).
FCA Comment: What is the basis for this? Where did the 20 feet or two channel lengths
come from? The Lacomb screen and the North Greenpoint screens both have a fairly radical
bend just upstream of the leading edge of the screen and both have performed well. For a
screen of 80 CFS, this requirement would call for a 300 foot straight flume before the screen.
This would add not only extraordinary cost but also create much more site disturbance while
creating greater distance for fish to travel to get back into the river or stream through the
bypass with no improvement to screen function. Also, this would be in direct conflict with
11.5.1.2 from the February 2008 NMFS Anadromous Salmonid Passage Facility Design which
states, “The screen location must be chosen to minimize the effects of the diversion on
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instream flows by placing the bypass outfall as close as biologically feasible (i.e., considering
minimizing length and optimizing the hydraulics of the bypass pipe) and practically feasible
to the point of diversion”.
11.6.1.7.7 Bypass Flow Depth: For horizontal screens, the bypass flow must pass over the
downstream end of the screen at a minimum depth of one foot.
FCA Comment: Is the USGS testing data being taken into account here? USGS Open-File
Report 2010-1042 evaluates the impact of water depth on salmonid smolts and fry and
concludes that a range of minimum depths of 15 to 20 cm (5.9 to 7.9 inches) could be
acceptable and that the screen flume interface is not an obstacle to fish passage at depths of
less than one foot. These tests were performed at the request of NMFS to determine
acceptable depth of water over the screen. As written, this requirement eliminates the
ability to screen most small diversions with a horizontal screen due to the much higher level
of bypass flow required. Quite often, small diversions have proper site attributes for a
horizontal screen to work well and have site attributes that make other technologies difficult
or impossible to utilize. The best available scientific data would point to horizontal screens
as an excellent tool for protection of endangered species at depths as low as 6 inches.
11.6.1.7.8 Bypass Flow Amount: Bypass flow is used for transporting fish and debris across
the plane of the screen and into the bypass. For diversion rates less than 100 cfs, about 15%
of the total diverted flow should be used as bypass flow for horizontal screens. For diversion
rates more than 100 cfs, about 10% of the total diverted flow should be used for bypass
flow for horizontal screens. The amount of bypass flow must be approved by NMFS
engineers.
FCA Comment: Where is the data supporting this requirement? As we have stated
previously, this requirement doesn’t match up with the other criteria. Providing a minimum
depth and minimum sweeping velocity gives a basis for calculating the minimum amount of
bypass flow that will be met by meeting the other criteria. As screens get larger, percentage
of bypass flow decreases. This requirement would mean removing larger amounts of water
from the stream than is absolutely necessary for proper screen function. The USGS report
also shows safe and effective fish passage by maintaining depth and sweeping velocity
requirements, not through a percentage of total flow. This represents one more example of
an unnecessary and conflicting requirement that is not supported by scientific data, and will
have the effect of making it nearly impossible to install a horizontal screen.
11.6.1.7.9 Diversion Shut-off: If inadequate bypass flow exists at any time (per Sections
11.6.1.7.8 and 11.6.1.7.9), the horizontal screen design must include an automated means to
shut off the diversion flow, or a means to route all diverted flow back to the originating
stream.
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11.6.1.7.10 Sediment Removal: The horizontal screen design must include means to simply
and directly remove sediment accumulations under the screen, without compromising the
integrity of the screen while water is being diverted.
FCA Comment: Why is this specifically called out here when section 11.10.1.7 of the current
criteria covers sediment management already where it says, “Provision must be made to limit
the build-up of sediment where it may impact screen operations”? Sediment accumulation in
front of a vertical screen is as much or more of an issue as it is with a horizontal screen and
therefore shouldn’t require redundancy.
11.6.1.7.11 Screen Approach Velocity: If a horizontal screen is not equipped with an
automated mechanical screen cleaning system, screen approach velocity must be less than
0.2 ft/s and uniform over the entire screen surface area. If equipped with an automated
mechanical screen cleaning system, screen approach velocity must be less than 0.4 ft/s and
uniform over the entire screen surface area.
FCA Comment: What is the definition of uniform here? As FCA has shown through
operational data and through the USGS biological testing, the approach velocity is not
uniform but instead is alternating between a positive and negative number. The oscillating
velocities found in the Farmers Screen greatly contribute to the self-cleaning characteristics
of the technology. The USGS biological testing has shown a high level of protection for
salmonid smolts and fry under these conditions. Section 11.6.1.1 (covering approach
velocity in the current criteria) makes no mention of the approach velocity being uniform
over the entire screen surface area. Why the difference here? Once again, ambiguity left to
individual interpretation will lead to differing application standards and could conceivably be
used to prohibit installation of any horizontal screens.
11.6.1.7.12 Screen Sweeping Velocity: For horizontal screens, sweeping velocity must
exceed twice the approach velocity and gradually increase for the entire length of screen.
Higher sweeping velocities may be required to achieve reliable debris removal and to keep
sediment mobilized. The design sweeping velocity must be consistent with successful
prototypes developed through conducted research. Sweeping velocity should never be less
than 2.5 ft/s, or an alternate minimum velocity based on an assessment of sediment load in
the water diversion system.
FCA Comment: The minimum sweeping velocity stated in this section as 2.5 ft/s makes sense
based on operational and biological testing data, however, as the USGS report states, a
sweeping velocity of twice the approach velocity would not be adequate and should be more
like 30 to 60 times the approach velocity. A sweeping velocity of twice the approach velocity
would also contradict the proposed maximum approach velocity of 0.2 ft/s in combination
with the minimum sweeping velocity of 2.5 ft/s. It is also not possible to have a sweeping
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velocity that gradually increases for the entire length of the screen without installing the
screen at a slope and therefore rendering the screen incapable of protecting fish or
managing debris. None of the prototypes or installed screens has this characteristic
including the Herman Creek screen where the biological testing was performed by USGS.
What is the basis for this requirement? A requirement that the sweeping velocity increase
along the length of the screen is not possible to achieve and therefore would make it
impossible to install a horizontal screen and still meet NMFS criteria.
11.6.1.7.13 Screen Approach Velocity: For horizontal screens, approach velocity and
sweeping velocity must work in tandem to allow self cleaning of the entire screen face and to
provide good bypass conditions. If this is has not been demonstrated by a prototype to be
hydraulically similar to the proposed design, the screen design must include retrofit
capability for an automated screen cleaning system.
FCA Comment: Why have two sections titled “Screen Approach Velocity”? Would this be
better if combined with section 11.6.1.7.11? Or rather, is this language meant to replace the
previous language?
11.6.1.7.14 Inspection and Maintenance: Daily inspection and maintenance must occur of
the screen and bypass to maintain operations consistent with these criteria.
FCA Comment: This is already addressed in sections 11.10.1.1 and 11.10.1.3 of the current
criteria.
11.6.1.7.15 Monitoring: Post construction monitoring of the facility must occur for at least
the first year of operation. This monitoring must occur whenever water is diverted, and
include a inspection log (in table form) of date and time, water depth at the bypass, debris
present on screen (including any sediment retained in the screen openings), fish observed
over the screen surface, operational adjustments made, maintenance performed and the
observer’s name. A copy of the inspection log must be provided annually to the NMFS
design reviewer, who will review operations and make recommendations for the next year
of operation.
Summary: It would appear that the NMFS requested biological testing results have not been
taken into account by NMFS staff. Some of the proposed criteria are impossible to meet and
many of them are so restrictive that it makes the vast majority of potential sites where a
horizontal screen could be the best available technology now off limits. Data gathered during 10
years of design, operation, and testing as well as results from installation, operation, and
evaluation of 21 Farmers Screens in a range of sizes and conditions seem to have been
summarily dismissed. Indications made in recent emails that this is considered by NMFS staff to
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be a final draft of the criteria document is distressing, given that there are so many
inconsistencies within the criteria, and so many instances where USGS biological testing results
appear to be in conflict with the resulting criteria they were intended to inform.
It is difficult not to conclude, given the contradictory and arbitrary nature of this document, that
NMFS intention is to prevent any Farmers Screens from being installed anywhere anadramous
fish are present.
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